1. Field of the Invention
The present invention relates to a process for preparing a non-cohesive coating layer useful in the production of microcapsules, a process for the production of the microcapsules comprising said process for preparing a noncohesive coating layer, and microcapsules prepared by said process therefor. More particularly, it relates to microcapsules which are prepared from an emulsion and may advantageously regenerate an emulsion in the living body. Such microcapsules are useful in the fields of pharmaceuticals, cosmetics and foods.
Microcapsules are very small particles or drops of solid, liquid, solution or suspension encapsulated in a coating layer of high molecular compounds. Recently, microcapsules have attracted considerable attention as a means for producing a solid preparation from a liquid active substance and as a means for producing a preparation which is stable to the surroundings from a substance which is unstable.
2. Discussion of Prior Art
The known process for the production of microcapsules is classified into (1) a mechanical or a physical process and (2) a chemical or a physicochemical process, in which a physicochemical process involving coacervate formation is known as the coacervation method. The latter method comprises three steps, i.e. (1) preparation of an adhesive coating layer by forming a coacervate phase, (2) stabilizing (or hardening) of the coating layer and (3) recovering powders (or drying). It is to be noted that, in the conventional process, the coating layer should be stabilized before recovering and the stabilization has been usually attained by hardening.
The conventional methods of hardening include physical treatment such as heating or cooling and treatment with chemicals such as formalin. Upon such treatment, the primarily formed sticky coating layer changes to a nonsticky insoluble matter which, however, is difficult to be disintegrated under such mild conditions as in a living body, and is difficult to quickly release its contents. Moreover, since the above hardening treatment takes a considerable time and results in undesirable remaining of chemicals used in hardening which may cause problems, the hardening procedure has been a bottleneck of the process for producing microcapsules by the coacervation methods.
Japanese Patent Publication (unexamined) No. 36540/1984 discloses a process for production of microcapsules which comprises recovering microcapsules in the form of powders without partial or complete hardening of a coating layer.
In this case, while the stabilizing step (2) may certainly be omitted, a great amount of powders such as starch is required to add as a powdering agent to a slurry of microcapsules following removal of a medium in which the coacervation is occurred. Moreover, when the thus obtained microcapsules are subjected to steps of drying and sieving out of the powdering agent to give powdery microcapsules, microcapsules thus prepared are not uniform in size and the microcapsules are not sufficiently fluidic. Thus the above mentioned method is disadvantageous in practical use.
As the result of an extensive study to overcome the above drawbacks and problems in the known coacervation method, it has now been discovered that when a certain kind of inorganic compound is used as a powdering agent, noncohesive and sufficiently fluidic microcapsules can be obtained without the stabilizing (hardening) step (2).